Tube drawing apparatus



Dec. 19, 1961 P. RUSSELL TUBE DRAWING APPARATUS Filed Feb. 18, 1959 INVENTOR. PETER RUSSELL dTTORNEYS Zfwa,

Patented Dec. 19, 1961 2 ice 3,013,652 TUBE DRAWING APPARATUS Peter Russell, Waterbury, Conn., assignor to Anaconda American Brass Company, a corporation of Ionnecticut Filed Feb. 18, 1959, Ser. No. 794,103 4 (Ilaims. (Cl. 205-7) This invention relates to tube drawing, and is particularly directed to the provision of improved apparatus for drawing tubes with the use of a floating plug and winding the drawn tube under tension on a drum. More particularly, the invention provides the combination with a floating plug of a mandrel attached thereto and extending therefrom through the tube to the point of tangency of the tube with the drum to prevent flattening of the tube as it is wound tightly under tension on the drum, or to control the degree and form of such flattening as is permitted to occur.

One of the more common methods of forming thinwalled tubing of the type employed in heat exchangers, air conditioning units and the like, is to draw the tube through a die by means of a blocker. The blocker is essentially a rotatable drum adapted to grip the end of the drawn tube on the exit side of the die, and to pull it through the die under considerable tension and wind it in a coil on the drum. Generally a floating plug is em ployed in cooperation with the die to define the desired inside diameter and Wall thickness of the tube being drawn.

In the drawing operation, the floating plug is first inserted into the tube and the end of the tube is pointed to permit it to be extended through the die orifice. The projecting end of the tube is attached to the circumference of the blocker, and the blocker is rotated to pull the tube through the die. The floating plug within the tube is thereby carried into the die orifice and becomes held therein in position to define the inside diameter and wall thickness to which the tube is drawn as the blocker continues to pull the tube through the die.

One significant disadvantage of this method is that as the drawn tube is wound onto the circumference of the blocker under tension, it is pressed so tightly thereagainst that it is extremely difficult to prevent flattening, particularly when any substantial reduction in tube diameter or wall thickness is effected in the drawing operation. The components of force on the tube radial to the blocker are particularly great at the point where the drawn tubing tangentially engages the circumference of the blocker, and such forces tend to flatten the tube particularly at that point. Relatively thin-walled round tubing is thus often deformed to a slightly oval shape as it is pulled through the die and wound up on the blocker drum.

It is a primary purpose of the present invention to provide a mandrel which lends support to the wall of I the tubing as it engages the blocker to prevent any substantial change in the dimensions defined by the die and plug, or to limit such change to a desired predetermined extent. This is accomplished in accordance with the invention without sacrificing the advantages of a floating plug, which permits the tubing to be drawn in extended or even continuous lengths. Means also are provided to enable the mandrel to be adapted to tubing of various inside diameters, and to be adjusted for use with blockers which are spaced at various distances from the die.

The invention provides the combination with a floating plug for use in tube drawing by pulling the tube over said plug and through a die orifice into which said plug extends and winding the tube under tension on a drum,

of a mandrel adapted to be inserted into the tube and having substantially the inside cross-sectional size and shape or" the tube. The mandrel is attached to the plug and is of sufficient length to extend through the drawn tube substantially to the point of tangential engagement of the tube with the circumference of the drum on which the tube is wound when the plug is operatively positioned in the die orifice. Thereby it prevents flattening of the tube as the tube is being wound under tension on the drum.

Preferably, the mandrel is of rather short length and is joined to the plug by a connecting rod of smaller crosssectional dimension than the mandrel itself. The mandrel advantageously is detachably secured to the connecting rod, and the connecting rod preferably is axially adjustable relative to the plug to permit adjustment of the distance from the plug to the rod of the mandrel.

A preferred embodiment of the mandrel provided by this invention is described hereinbelow with reference to the accompanying drawings, wherein:

FIG. 1 is a sectional elevation showing a tube being drawn through a die over a floating plug and wound on a blocker drum, with the mandrel of this invention operatively positioned in the tube; and

FIG. 2 is a schematic sectional elevation of tube drawing apparatus in which the mandrel is employed.

Only the basic elements of the tube drawing apparatus are shown in FIG. 2, namely a frame 10, a drawing die assembly 11 mounted therein, and a blocker 12. In the die assembly 11, a die 13 defining a tapered die orifice 14 is held firmly in place in an annular die block 15. The blocker 12 includes a cylindrical drum 17 rotatably mounted upon a shaft 18. Any convenient driving means may be provided for imparting rotation to the blocker shaft. Means are also included in the blocker for attaching the end of the tubing to the circumference of the drum 17 as, for example, a cable 21 anchored at one end to the drum and adapted to receive the end of the tubing in jaws 23 at the other end. An undrawn tube 25 is delivered to the drawing die assembly 11 from any conventional reserve coil on the entrance side of the die, and it emerges from the die assembly 11 as a drawn tube 26 on the exit side of the die.

To define and maintain the desired inside diameter of the drawn tube 26, and to control its wall thickness, a tapered plug '27 is disposed in the tube within the die recess. The plug 27 is of the usual form, including a nose portion 28 conforming to the desired inside diameter of the drawn tubing, a tapered section 29 which seats adjacent the entrance flair of the die orifice, and a rear section 30. The diameter of the rear section 30 of the plug is smaller than the inside diameter of the undrawn tube 25, to permit the plug to be easily inserted into the open end of the tube 25. The plug 27 is provided with an internally threaded longitudinal bore 31 extending coaxially through its entire length.

Attached to the plug 27 is a connecting rod 33 which is externally threaded at both ends. One end portion 34 of the connecting rod is threaded for a distance greater than the axial length of the plug 27, and extends into the bore 31 of the plug in threaded engagement therewith.

By screwing the rod in or out, it can be moved longitudinally relative to the plug, or it can be replaced by a different rod. A lock nut 35 is provided to permit the plug 27 to be locked in engagement with the rod at any desired position along its threaded end Portion 34.

At the opposite end of the connecting rod 33 is another threaded portion 37. This end is engaged in a threaded hole 38 in a sizing mandrel 39, so that the mandrel is attached in fixed position relative to the rod 33 and plug 27. The mandrel 39 is shaped to conform closely with the inside diameter of the drawn tube 25. Since it is removably threaded onto the rod 33, it can be replaced when desired.

When the mandrel 39 and connecting rod 33 are operatively mounted in the tube drawing device, their combined lengths enable them to extend through the drawn tube 26 from the drawing die assembly 11 to the point where the tube 26 tangentially engages the circumference of the drum 17. At that point the sizing mandrel 39 is defined by a rounded or otherwise suitably shaped end 40. The position of the rounded end 46 of the sizing mandrel 39 relative to the plug member 30 may be adjusted to accommodate different distances between the drawing die and blocker drum by changing the position of the threaded end portion 34 of the rod 33 in the plug 27.

In the operation of the apparatus described, the floating plug with the mandrel attached thereto is inserted into the open end of a length of undrawn tube 25 with the plug member 30 innermost. The open end of the tube 25 is then pointed to permit inserting it through the die orifice 14 and to project beyond the die 13. The projecting end of the tube is then pulled far enough through the die so that it may be gripped in the jaws 23, and the drum 17 then is rotated on the shaft 18. This causes the drawn tube 26 to be pulled through the die assembly 11 and wound under tension in the drum. At the same time, the floating plug within the undrawn tube 25 moves into the die orifice 14 until its tapered section 25- seats against the portion of the tube being drawn down into the flair of the die orifice, in the position shown in FIG. 1.

At this point, the rounded end 46 of the sizing mandrel 39 extends substantially to the point of tangency between the drawn tube 26 and the circumference of the drum 17. The tube 26 is under great tension as it is wound onto the blocker 12 but is prevented from collapsing or deforming as a result of the rigid internal support given to its walls by the mandrel 39 snugly fitting therewithin. This support continues up to the point where the drawn tube 26 engages the circumference of the drum 17 or any previously wound turns of the tube, whereupon the tension on the tube 26 is relieved to a considerable degree by the frictional engagement with the drum or the previous turns. Thus, the desired dimensions are maintained as the drawn tube 26 is wound on the blocker drum, and the tube on the drum has substantially the same dimensions and shape as when it emerges from the die.

It is of course apparent that by suitably shaping the end 40 of the mandrel 39, it is possible to effect a controlled and limited degree of flattening of the drawn tubing, in cases where it is desired to produce a tube of oval or other flattened cross section. In such cases the radially compressive forces exerted on the tube at the point of tangency with the drum are allowed to cause the tube to flatten, and the mandrel assures that such flattening is limited to the desired degree so that the desired final tube cross-sectional shape is attained.

I claim:

1. The combination with a floating plug for use in tube drawing by pulling the tube over said plug and through a die orifice into which said plug extends and then in a substantially straight line from said die orifice to a drum where it is wound under tension, of a mandrel adapted to be inserted into said tube and having substantially the inside cross-sectional size and shape of the drawn tube,

and a substantially straight rigid connecting rod of smaller cross-sectional dimensions than said mandrel affixed at one end to the mandrel and at the other end to said plug, adjustable means included in said connecting rod permitting said mandrel to be moved longitudinally to various fixed positions relative to said plug, the combined length of said mandrel and connecting rod being suflicient to extend longitudinally in a substantially straight line through the tube Substantially to the point of tangential engagement of the tube with the circumference of the drum when the plug is operatively positioned in the die orifice, whereby said mandrel prevents undesired flattening of the tube as the tube is being wound under tension on the drum.

2. The combination with a floating plug for use in tube drawing by pulling the tube over said plug and through a die orifice into which said plug extends and then in a straight line from said die orifice to a drum where it is wound under tension, of a mandrel adapted to be inserted into said tube and having substantially the inside cross-sectional size and shape of the drawn tube, and a straight rigid connecting rod of smaller cross-sectional dimensions than said mandrel affixed at one end to the mandrel and removably attached at the other end to said plug, adjustable means included in said connecting rod permitting said mandrel to be moved longitudinally to various fixed positions relative to said plug, the combined length of said mandrel and connecting rod being suflicient to extend longitudinally in a straight line through the tube substantially to the point of tangential engagement of the tube with the circumference of the drum when the plug is operatively positioned in the die orifice, whereby said mandrel prevents undesired flattening of the tube as the tube is being wound under tension on the drum.

3. The combination with a floating plug for use in tube drawing by pulling the tube over said plug and through a die orifice into which said plug extends and then in a straight line from said die orifice to a drum where it is wound under tension, of a mandrel adapted to be inserted into said tube and having substantially the inside cross-sectional size and shape of the drawn tube, a straight rigid connecting rod of smaller cross-sectional dimensions than said mandrel, said plug having an internally threaded bore extending longitudinally therethrough, one end of said connecting rod being threaded and extending through the bore in said plug in threaded engagement therewith, locking means for atfixing said plug at various longitudinal positions along the threaded end portion of said connecting rod, the other end of said connecting rod being removably attached to said mandrel, the combined length of said mandrel and connecting rod being sufficient to extend longitudinally in a straight line through the tube substantially to the point of tangential engagement of the tube with the circumference of the drum when the plug is operatively positioned in the die orifice, whereby said mandrel prevents undesired flattening of the tube as the tube is being wound under tension on the drum.

4. The combination with a floating plug for use in tube drawing by pulling the tube over said plug and through a die orifice into which said plug extends and then in a straight line from said die orifice to a drum where it is wound under tension, of a mandrel adapted to be inserted into said tube and having substantially the inside crosssectional size and shape of the drawn tube, a straight rigid connecting rod of smaller cross-sectional dimensions than said mandrel, said plug having an internally threaded bore extending longitudinally therethrough, one end of said connecting rod being threaded for a distance greater than the longitudinal dimension of said plug and extending through the bore in said plug in threaded engagement therewith, locking means for affixing said plug at various longitudinal positions along the threaded end portion of said connecting rod, the other end of said connecting rod being removably attached to said mandrel,

References Cited in the file of this patent UNITED STATES PATENTS Farrell June 5, 1883 Lowe Dec. 25, 1923 Roth Oct. 25, 1955 FOREIGN PATENTS Germany May 17, 1954 

